This invention relates generally to methods and apparatus for running wireline tools on coil tubing and, more specifically, to methods and apparatus for coupling wireline tools to coil tubing.
It is common practice to drill wells in exploration for oil and gas with a portion of the bore deviating from vertical orientation. The deviation or inclination may extend for a considerable distance, sometimes returning to the usual vertical orientation. It is well known in the art of drilling such wells to attempt to log or perforate the formations surrounding such boreholes with instruments run into the well bore on an electrical wireline to perform various operations. Such tools usually depend upon the force of gravity to become positioned within the well bore.
Manifestly, the relatively horizontal angle of the deviated portion of the well bore will not permit the wireline conveyed tools to move into and through the deviated portion since friction of the tool on the deviated portion works against the force of gravity. In the past, numerous specialized methods and devices for assisting the wireline conveyed tools through deviated portions of a well bore have been suggested. Examples of such devices are illustrated in U.S. Pat. Nos. 4,457,370, showing a system for running a tool coupled directly to a string of drill pipe; 4,082,144, illustrating a mechanical device attached to the tool to assist descent; and 3,401,749, describing a system of running a tool coupled to a relatively flexible conduit, commonly referred to as "coil tubing".
A typical logging or perforation operation using coil tubing includes a system where an electric wireline is inserted through a length of conduit and connected to a tool at the distal end of the conduit. The tool, wireline and conduit are extended into the well bore by winding the conduit from a coil tubing unit located at the earth's surface. An example of one method for coupling a tool to the tubing can be found in U.S. Pat. No. 4,612,984, which is incorporated herein by reference.
An inherent problem when running any tool in a well is that it may become stuck. The presence of sand or other debris is just one of several causes of such difficulty, and the problem is especially critical in a deviated well. The "pull-out" devices presently known in the art do not furnish an adequate solution to such problem; however, as those devices are directed primarily to tools attached only to a wireline and lowered thereon into the well by means of gravity. An example of such a device is found in U.S. Pat. No. 4,648,444. Devices such as the aforesaid, for use with a gravity-feed wireline, allow separation of the wireline (or cable) and cable head from the tool through the exertion of tension on the cable from the earth's surface. Once the cable and cable head are removed from the well, a fishing tool is lowered into the well for the purpose of securely grasping, and hopefully, dislodging the jammed logging tool.
Such wireline pull-outs are not, however, particularly useful in connection with coil tubing deployed in a deviated hole and/or in logging operations where the well is flowing during logging. If the well is flowing during logging, it is desirable to attach coil tubing to a logging tool in a fluid tight, occlusive manner. Otherwise, temporary increases, or "spikes", of pressure in the bore hole can send damaging fluid up into the coil tubing. Consequently, use of a typical wireline pull-out with coil tubing conveyed tools is inappropriate because merely effecting separation of the tubing from the tool would allow the intrusion of bore hole fluids into the coil tubing, an event which frequently negates much of the advantage in using coil tubing in the first place.
One feature of this invention is, therefore, to provide methods and apparatus for connecting a wireline tool to coil tubing in such manner that the connection is fluid occlusive and the interior of the tubing is protected from pressure spikes, but that the tool can be surely and conveniently separated from the tubing should the tool become stuck downhole; and another of the several features of this invention is to provide methods and apparatus for such separation which preserves the integrity of the tubing and prevents the intrusion of bore hole fluids therein.